As is well known to those having skill in the art, monocrystalline silicon carbide is particularly well suited for use in semiconductor devices, such as integrated circuit semiconductor devices and power semiconductor devices. Integrated circuit semiconductor devices typically include many active devices such as transistors in a single semiconductor substrate. Power semiconductor devices, which may be integrated circuit devices, are semiconductor devices which carry large currents and/or support high voltages.
Silicon carbide has a wide bandgap, a high melting point, a low dielectric constant, a high breakdown field strength, a high thermal conductivity and a high saturated electron drift velocity compared to silicon, which is the most commonly used semiconductor material. These characteristics allow silicon carbide microelectronic devices to operate at higher temperatures and higher power levels than conventional silicon based devices. In addition to the above advantages, silicon carbide power devices can operate with lower specific on-resistance than conventional silicon power devices. Some of the advantages of using silicon carbide for forming power semiconductor devices are described in articles by K. Shenai, R. S. Scott and inventor B. J. Baliga, entitled Optimum Semiconductors for High-Power Electronics, IEEE Transactions on Electron Devices, Vol. 36, No. 9, pp. 1811-1823 (1989); and by M. Bhatnagar and inventor B. J. Baliga entitled Analysis of Silicon Carbide Power Device Performance, ISPSD '91, Abstr. 8.3, pp 176-180 (1991).
In particular, semiconductor devices such as silicon carbide power MOSFETs have been considered attractive candidates for high power applications because the resistance of the MOSFET drift region is 200 times smaller than that for silicon devices with the same breakdown voltage. However, the operation of some silicon carbide power devices may require the formation of an inversion layer channel when turned on. This is unfortunate because the inversion layer mobility measured for electron inversion layers has been found to be relatively small (.about.15 cm.sup.2 V.sup.-1 sec.sup.-1). This will result in a relatively large channel resistance which can degrade performance of the silicon carbide power device. Thus, notwithstanding the benefits of using silicon carbide as a semiconductor material, there continues to be a need for silicon carbide semiconductor devices which do not require the formation of inversion layer channels when turned on. Examples of such devices are disclosed in U.S. Pat. Nos. 5,323,040, and 5,396,085 to Baliga, entitled Silicon Carbide Field Effect Device and Silicon Carbide Switching Device With Rectifying Gate, the disclosures of which are incorporated herein by reference. These devices may, however, require the formation of vertically walled trenches in silicon carbide and relatively high resolution lithographic steps during processing, which makes these devices difficult and/or expensive to produce.
Many of the methods for forming semiconductor devices also require the formation of insulating regions, such as oxides, that act as masks for device processing, perform the function of electrically isolating one or more regions of a semiconductor device as well as isolating adjacent devices on a semiconductor substrate. Conventional techniques for forming insulating regions on silicon include thermal oxidation, low pressure chemical vapor deposition (LPCVD) and plasma-assisted deposition. As will be understood by one skilled in the art, thermal oxidation is probably the most common technique used to grow high quality oxides, such as those made of SiO.sub.2, on silicon substrates. SIMOX techniques have also been successfully used to form silicon SOI substrates.
Notwithstanding these attempts at growing insulating regions in silicon, however, similar techniques have not found substantial application in the formation of insulating regions in silicon carbide devices. This is particularly true with respect to the formation of relatively thick insulating regions. As will be understood by those skilled in the art, thick insulating regions are particularly important for silicon carbide power devices in order to inhibit leakage currents, electric arcing, or field oxide breakdown, when such devices are operated in the presence of high electric fields and/or at high current levels. Thus, there continues to be a need for a method of forming silicon carbide devices which have insulating regions therein that provide electrical isolation and inhibit leakage currents.